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MG MG Y Type - Fitting a waxstat.

My YA has been running for at least the last 10 years and two owners with no thermostat.I'm told by the last owner that the by-pass out of the (empty) thermostat housing is blocked off.There is no heater fitted.
The car ran at 60-70 degrees C seldom hotter so I have started to blank off the radiator progressively with 2mm clear plastic sheet, 3 per side which is shuffled behind the radiator shell and in front of the slats. This works fine and by addind or removing some of the 6 pieces the temperature will rise nicely to 80-90 deg, but as the weather temperature changes the blanking needs alterig. All a bit of a drag.
I had a heap of good advice from Neil Cairns on fitting a modern waxstat (and see Living with the XPAG, by Neil) but the aperture in the waxstat when open is so small compared with the empty system that I am having second thoughts.He advises that the by-pass should remain blocked-off.
I have a spare elbow fitted with a waxstat but before I go through the rigmarole of draining, dismantling, refitting, and then finding the car overheats, has anyone got experience of this situation?
Second, Can someone explain why the by-pass has to be blanked off? It is so much smaller than the main system that I am tempted to un-blank it so as to give a bit more flow than the waxstat. Is there a reason why this is a bad idea?
Michael Nicholson

Michael,

Please fit a waxstat as per Neils' instructions. The engine will warm much quicker and run better for it, without washing off all the precious oil in the cilinder-bores.

The by-pass is to provide some flow in the system whilst the original thermostat is closed. The original sleeve-type closed this by-pass when it opened up to the radiator.

If you don't blank it, especially with an old radiator that is becoming clogged with silt etc, the hot water will take the way of least resistance through the by-pass instead of the radiator. This won't improve cooling!

Blank the by-pass or put a restrictor with a small hole in it.
Willem van der Veer

I followed Neil's advice to the letter when fitting a Smiths Heater and now have a very efficiet heating system and have never over heated. I found a suitable stat by checking through Halfords stock. I think the final chioice was for a Fiat but had to be filed around the edge to make it a good fit
Peter Vielvoye

Michael,
Just to push you further towards fitting a waxstat: most (MGB)racers don't have a thermostat, but they do fit a restrictor in place to ensure proper coolant flow to rear cilinders. I'm not sure if this is the case with the XPAG-system, but generally it is bad practise to run without a (restricting) thermostat.
Willem van der Veer

Just a few words of thanks for the encouragement and advice given in this forum and elsewhere.

I fitted a waxstat as advised between the old thermostat housing and the elbow below it with some reservations because the waterway with the thermostat open is so much smaller than the empty pipe.

Tried it today on a brisk 15 mile run with traffic and hills and didn't exceed 80 deg.C with air temperature about 15 deg.C. I was hoping for a bit higher, but the thermostat is either 74 or 78 deg.C, as advised, I forget which, which seems to prove that it's working about right I suppose.



Michael Nicholson

So many spare parts forthe XPAG are remanufactured - why isn't the original type thermostat with blanking-off sleeve ?
Remo Peter

Remo,

It is. See Moss Motors part number 434-168. Moss Europe shows this as:
434-168 THERMOSTAT & HOUSING TA, TB, TC, TD with 2 prices of £36.95 and €54.69.

Moss USA is a little fuller in its options:
434-168 $129.95 THERMOSTAT & HOUSING Note: Repro. of orig. cast iron type with non-removable thermostat TC-TD, but also offers,
434-178 $154.95 THERMOSTAT & HOUSING Note: replacement with replaceable thermostat; looks original. TC-TD, as well as
434-200 $13.40 THERMOSTAT, replacement Note: Fits replacement Thermostat Housing 434-178 only! TC-TD with 434-178 replacement housing.

My understanding of the Moss USA is that you can replace the entire cast housing with either a replacable, or a non-replacable thermostat, whereas Moss Europe only offers the modern replacable unit. Check with the supplier to confirm this though before ordering.

Paul
Paul Barrow

I didn't have to buy any expensive housing, although the cost of the bits for tha temperature gauge was costly as it included a 5/8 inch BSP tap and tapping drill whose cost was too expensively embarassing to mention.
The thermostat cost me about £10 (GBP10)and was for a Datsun but I've lost the details.I took a thermostat that cost £1 at an autojumble as a pattern. It was the right outside size but too hot. I had to drill the flange to allow a small water flow when closed, and trim part of the unit where it fouled in the elbow.

Michael
Michael Nicholson

Dear Paul
I've been told all Moss replacement thermostats are of the modern (wax) type. But only the expanding brass bellows type is able to have the blank-off sleeve moving with the valve. Now I'm confused !

Dear Michael
Is your Datsun model a waxstat or a bellows ?
Remo Peter

This thread was discussed between 01/09/2007 and 02/10/2007

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